1. Field of the Invention
This invention relates to photographic silver halide elements having improved speed and increased sharpness in halftone images when developed in hydroquinone developers.
2. Description of the Prior Art
Hunt U.S. Pat. No. 3,249,440 patented May 3, 1966 is directed to the use of molecular iodine in radiation-sensitive, direct-writing, light-developable silver halide emulsion layers.
Duennebier et al. U.S. Pat. No. 3,297,445 patented May 10, 1967 deals with inhibitor releasing developers which are incorporated in the emulsion layers or in hydrophilic layers contiguous thereto and comprise iodoquinones. The compounds are alleged to release iodine at or near the site of development when reacted with sulfite ions although the reactions shown appear to contradict this in that only iodide ions are shown to be released.
De Munch et al., U.S. Pat. No. 3,617,284 patented Nov. 2, 1971 describes a process of developing a lith-type negative silver halide emulsion in the presence of an N-vinyl-2-pyrrolidone polymer with hydroquinone developer containing alkylene oxide units. The iodine complexes of the polymer may also be used and the polymers may be incorporated in either the emulsion layer or a layer contiguous with the emulsion layer. The iodine complexes are described as addition complexes (addition by inclusion) of molecular iodine with the N-vinyl-2-pyrrolidone polymer.
Milton, U.S. Pat. No. 3,697,281 patented Oct. 10, 1972 describes the use of strong oxidizing agents in fogged direct-positive emulsions for improved speed vs. maximum density characteristics.